Abstract
Filamentous fungi were used to leach heavy metals from dredged sediments in semi-pilot scale air-lift bioreactors. Prior to the bioleaching experiments, a physico-chemical characterization of the sediments comprising a sequential extraction study was conducted. The sediments turned out to highly contaminated with heavy metals. Most of the studied metals were found to be strongly linked to the matrix because of their association with the sulphides and with the organic matter. The conditions that favored the solubilization of heavy metals by the filamentous fungi turned out to be favorable for the activity of the sediments organotrophic bacterial microflora as well. The latter played a key role in the biosolubilization process by producing organic acids under temporary anoxic conditions. Better solubilization results (Mn: 77%, Zn: 44%, Cu: 12%, Cd and Pb: <2%) were thus obtained in the uninoculated sugar treatment in comparison to the fungal treatment. In general, organotrophic leaching was found to be limited by the poor nature of the organic acids and by their microbial consumption under sugar limited conditions. It was therefore restrained to the relatively mobile metals, namely those linked to the acid-soluble and reducible fractions of the sediments.
Highlights
The Nord-Pas de Calais region in France suffers from an important pollution of its water streams as a result of its extensive past industrial activities
To assess the level of contamination and in the absence of French standards specific for sediments, the total concentrations of heavy metals were compared to the French soil standards, which are values above which, no sediment or sludge application is allowed on a given soil
No legislation exists at the present time for Mn, we can notice the high load of the sediments in this metal as its concentration is superior to the Natural Values, which are values below which a given soil is considered as not polluted
Summary
The Nord-Pas de Calais region in France suffers from an important pollution of its water streams as a result of its extensive past industrial activities. Large volumes of sediments are formed in the rivers every year. These sediments have to dredged periodically in order to prevent floods and navigation problems. According to the French Water Agency, more than 1 million m3 of sediments have to be dredged each year [1]. One third of this volume is polluted. At the mean time, confined disposal is the most commonly used sediments treatment technique. It is limited by the availability of confinement spaces and by its elevated cost. Physico-chemical techniques such as chelation or vitrification are limited by their high costs and by the potential loss of the sediments properties [2]
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